This invention relates to the art of braking systems, and more particularly to a trailer antilock brake system (ABS) modulator valve. The invention is particularly applicable to a tractor-trailer type vehicle equipped with an air braking system in which a vehicle operator generates a control signal to operate a brake control valve. The signal is transmitted to relay valves which, in response, communicate compressed air from storage reservoirs to vehicle brakes. It will be appreciated, however, that the invention may relate to similar environments and applications.
ABS brakes for these types of systems typically include an impermeable or solid walled piston or flexible diaphragm that selectively moves during normal service braking to establish communication with an exhaust passage. Although providing for effective normal service braking, the control line and control volume disposed on one side of the piston or diaphragm of an ABS modulator is less frequently in communication with an ABS exhaust passage. Since air is involved, moisture is always an attendant consideration. In other words, moisture can build up and remain in the control volume. Since ABS braking is less frequently used, the potential exists for blockage to occur at the ABS exhaust passage which is not desirable. The exhaust passage is necessarily exposed to ambient conditions such as ice, mud, etc., and if the exhaust passage is not frequently used, the passage could be less effective than desired.
On the other hand, normal service braking is frequently and necessarily employed. The separate exhaust passage associated with normal service braking in known vehicles has less problems associated with ice or mud since, whenever a brake application is released, the exhaust passage is used and likewise ice or mud expelled therefrom.
Known modulators also have an extended or longer exhaust passage since separate exhaust passages were used for normal service braking and ABS control events. Longer exhaust passages result in reduced response time during normal service braking.
Alternatively, known ABS braking systems for tractor trailer type vehicles are commercially successful and have been widely adopted and accepted in the industry. Thus, any improvement that addresses these concerns would necessarily be attractive if can be easily incorporated into the existing structure without substantial modification.